This disclosure relates generally to map matched vehicle trajectories, and more specifically to measuring the accuracy of map matched trajectories.
A transport service system evaluates the accuracy of map matching processes used to determine the most likely trajectory of a transport vehicle. Map matching is the process in which raw location signals, such as global positioning satellite (GPS) coordinates, are “snapped” to the underlying road segments. That is, for a given location signal or for a series of location signals, the map matching process attempts to identify a position on a road or road segment given the map data corresponding to the location signal. The transport service system uses the map matched road or road segments to determine transit information, such as the on-route distance of a trip or identifying the location of a vehicle for routing to a destination.
The map matching process may incorrectly identify the road segments actually traveled by a vehicle for a variety of reasons. First, the location signals are typically derived from sensors on a vehicle, which may be affected by interference from buildings, vehicles, weather, and other circumstances which affect the precision of the location signals. Second, the map data used by the transport service system typically associates location coordinates (such as a specific latitude and longitude) with the various road segments. In some cases, the map data may include incorrect location coordinates for a road segment that does not reflect the true coordinates of that road segment in the world. The map data may describe roads that do not actually exist, or there may be existing roads that are not captured by the map data. In addition, the map matching process itself for selecting possible road segments may poorly reflect the actual roads traveled by a vehicle.